The Pentagon will consider overhauling the process for granting security clearances and access to military installations in response to the shooting at the Washington Navy Yard involving a former sailor who killed 12 people.

The Defense Department has launched three separate investigations into the Sept. 16 mass shooting, with a focus on whether systemic flaws or failures contributed to the incident involving Aaron Alexis, 34, a former aviation electricians mate third class and contractor with a security clearance who worked at the headquarters of Naval Sea Systems Command.

The investigations come after reports that the federal contractors who conducted Aaron’s background check in 2007 knew that his criminal record included an arrest for a gun-related incident but downplayed the incident in a report to the Navy.

Deputy Defense Secretary Ash Carter said the sheer volume of people with security clearances raises questions about the current system.

“The volume is huge. There are millions of Americans who have security clearances, many millions. And they are necessary to accomplish the government’s security business. There are many more who have access to our DoD installations and facilities,” Carter said at a press briefing Wednesday.

“The volume is very high and I think one of the issues that we are going to look at both inside the department and in the governmentwide review is how do you do, for such large numbers of people, a thorough and careful job so that you have a reasonably good chance of surfacing a propensity to violence or to some other kind of behavior before that behavior occurs?” Carter said.

Defense Secretary Chuck Hagel has launched an investigation to be led by Undersecretary of Defense for Intelligence Michael Vickers. That will focus on base security and the security clearance process and it will be completed this fall.

A separate independent panel will also review the incident and consider similar issues. That will be led by Paul Stockton, a former top official at the Department of Homeland Security who also helped lead a probe into the Fort Hood shooting in 2009. The independent panel will also be led by retired Adm. Eric Olsen, a former head of U.S. Special Operations Command.

The Department of the Navy will also conduct a review of the incident. All three reviews will be provided to Hagel for a final assessment in December.